insulating a large shed / summerhouse

7 May 2010
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United Kingdom
I have just had a 15'x10' apex roof shed erected today. construction appears to be pse 2 3/4" x 1 3/4" treated studwork. treated 13mm shiplap walls & 15mm t&g roof. All sits on 18mm treated timber base on treated timber bearers approx 2x2.

I had a concrete base constructed before hand which the shed now sits on but base is larger than the shed. I have now read that the bearers should sit on a dpm in this case but its too heavy to change now.
Also would've like to lay an extra row of bearers in opp direction before it went down but didnt get chance.

before i ask about insulation i noticed a poss issue today in heavy rain. Moisture was being drawn up into the timber studs at the base & into the edges of the timber floor boards.
Seems maybe the water was running off the roof then splashing up off the concrete base on to the sawn edges on the floor boards which then absorbed along the boards a few inches into the shed.
The boards are treated & once the rain stopped they started to dry out.

Not sure how to rectify this or if this is normal. Maybe some guttering will catch the rain & stop most of it. Maybe i could construct a small skirt around the base?

Anyway onto insulating the shed. with the moisture in the floor issue just mentioned my plan for the floor was to:
1. board out floor with 25mm polystyrene or similar.
2. lay a thick dpm membrane.
3. lay a t&g floor system.
4. Lay lino
Should i use osb over chipboard or is there a better product for this?

for the ceiling & walls (studwork being 2 3/4")
1. use a superfoil quilt type insulation & tape it up to act as dpm.
2. osb or ply board over insulation.

Should i add battens before boarding out?

or should i just batten out studwork for extra depth & use kingspan type boards in between studwork?

Leaving aside windows & doors this will give me an airtight inside space, should i add some vents, if so where?

If i use kingspan inbetween the studwork do i fill the whole space or leave an airgap between the o/s wall & ins or between inside board & ins? will the shiplap vent itself or do i need to add breather holes in each studwork partition?

any advice appreciated
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gutter will be my first course off action

temporary plank along the sides angled at 45 degrees will bounce the water sideways

how much bigger than the shed is the base??
the front has only a bricks worth of over hang. the side are approx 5" to 12" as garden is not square & rear has about 8" gap. my garden is only 16' wide and shed & base takes up whole rear of garden so there is a 6' fenace around the back & sides.
I had a shed put up yesterday 12 ft by 10ft. It was raining when they put it up so the floor got wet. Last night there was a storm and when I looked in the shed the floor was only wet around some of the edges. I noticed that the outer wall didn't seem long enough as it didn't completely protect the floorboards from the rain. I am going to put mastic all round the lower outer edges to seal the bottom of the walls and the the floor.
I am going to add gutters because the rain has splashed mud up the outer walls.
The painted treatment seems very inadequate so I'll have to repaint it all including the ends of the beams on which the shed is laid.
As for insulating the walls and roof I think the best thing would be to put up thin batons against the outer walls (shiplap) place kingspan or other insulating boards against the batons and then cover with shiplap on the inside.I think the batons will be needed to allow for air circulation, but advice on this would be appreciated. Do I really need to allow for air circulation on the outer walls? I'm going to treat the roof in the same way.
For the floor I will lay that stuff that you put under laminate flooring to insulate and protect from damp (for concrete floors) and then laminate the floor.
BEFORE I start can anyone foresee any problems with my ideas?
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laminate is not a good choice
you need to use breathable builders membrane to allow it to breath

the side off the building must protect the floor or it will stay wet
if the grooves are at the bottom you may be able to add another part or full board to protect the floor but leave a gap for air to circulate

you need at least 3 coats of protection and 2 every 2 or 3 years to make it last a lifetime
Thanks. I asked my local timber merchant to cut the appropriate wood and I added it to the bottom of the walls. It has rained constantly since but no water gets into the shed :D .

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